Electronic devices include a variety of kinds, and most of them ape not resistant against the environment as they are. That is, if exposed as such in the air, a device undergoes deterioration by moisture, oxygen or other corrosive substances in the air and reduces its functions.
Among such delicate devices are included semiconductor devices such as IC, LSI, transistors, And diodes; piezoelectric devices; oscillators; condensers; and resistors.
These devices do not withstand long-term use stably unless some protection against the environment is afforded. Protection is, in principle, to prevent a device from being exposed directly to air and includes various means, from simple coating to packaging, i.e., perfect hermetic sealing, selected according to the type of the device, the purpose of protection or the degree of desired protection.
Of these protecting means, a "package" is important. While "package" in general covers a considerably broad concept, the term "package" as used herein means a hollow container, comprising a body in which a device is to be put and a cap or lid for covering the body, the body and the cap or lid being hermetically sealed.
The above-mentioned package has a sealing part at which the body and the cap or lid are adhered to each other, and this part has great influences on the airtightness of the whole package.
A widely used method for hermetically sealing the body and the cap or lid is "adhesion" in its broad sense. The term "adhesion" in its broad sense embraces not only mere adhesion with an adhesive but welding and fusing.
Where sealed areas are made of metal, they may be subjected to welding or silver soldering. Sealed areas made of ceramic or glass may be fused together with a glassy adhesive. Resin adhesives may be used irrespective of the material to be adhered.
However, the former two methods mentioned above require heating to such a high temperature that the device might be damaged, and are therefore unsuitable to those devices which are easily deteriorated at high temperatures. Besides, these methods incur high cost.
Adhesion with a resin adhesive is preferred for the low sealing temperature and the low sealing cost but has a disadvantage of low retention of airtightness, in particular, low impermeability to moisture. Therefore, resin adhesives have not yet been widespread in those packages requiring long-term reliability.